Plungers are employed to facilitate removal of gas from oilfield wells, addressing challenges incurred by “liquid loading.” In general, a well may produce liquid and gaseous elements. When gas flow rates are high, the gas carries the liquid out of the well as the gas rises. However, as well pressure decreases, the flowrate of the gas decreases to a point below which the gas fails to carry the heavier liquids to the surface. The liquids thus fall back to the bottom of the well, exerting back-pressure on the formation, and thereby loading the well.
Plungers alleviate such loading by assisting in removing liquid and gas from the well, e.g., in situations where the ratio of liquid to gas is high. In operation, the plunger descends to the bottom of the well, where the loading fluid is picked up by the plunger and is brought to the surface as the plunger ascends in the well. The plunger may also keep the production tubing free of paraffin, salt, or scale build-up.
One type of plunger is known as a “pad-type” plunger. Generally, these types of plungers include one or more sets of radially expandable sealing pads. The sealing pads may be biased radially-outwards, and may thus expand to engage the production tubing, and form a partial seal therewith. However, one issue with such plungers is that fluids may be able to flow past the plunger in the space radially between the pads and the center body or “mandrel” to which the pads are attached, and/or in spaces between the expandable pads. Furthermore, the pads are typically cast-formed, which may also allow for fluid flow past the plunger, between the pads and the production tubing. As such, the seal may be far from fluid tight. While some fluid flow past the plunger may be desired, e.g., to hasten descent, it may be desired to minimize the flow rate past the plunger, e.g., to maximize production and increase efficiency.